1. Field of the Invention
The present invention relates to a variable valve-actuating system for a four-stroke engine of a vehicle such as a motorcycle, and to an engine incorporating same. More particularly, the present invention relates to a variable valve-actuating system including a camshaft having a pair of cams operatively associated with an engine valve, allowing one of the cams to be selectively used for opening and closing operations of the engine valve, and to a method of using same.
2. Description of the Background Art
There are number of known variable valve-actuating systems for internal combustion engines. Generally, such valve-actuating systems include a rocker arm shaft and a rocker arm. The rocker arm shaft is arranged in parallel with a camshaft having a pair of cams. The rocker arm is supported on the rocker arm shaft to be swingable about the axis of the rocker arm shaft, and is concurrently movable in the axial direction thereof.
In accordance with a rotational movement of the camshaft, the rocker arm abuts on one of the cams so as to be swung, thereby causing the engine valve to perform the opening and closing operations. Concurrently, the rocker arm is moved in the axial direction, as appropriate, so that one of the cams can be used for opening and closing the engine valve.
An example of such variable valve-actuating system for an internal combustion is disclosed in the Japanese Patent Application Laid-open No. 2001-20710.
Recently, there has been a demand that the engine respond smoothly to an operational request made by a driver of a vehicle to the engine during operation thereof. However, in the conventional technique such as disclosed in the Japanese Patent Application Laid-open No. 2001-20710, a foreign object may possibly be attached (or get attached during the engine operation) to the outer peripheral surface of the rocker arm shaft, on which the rocker arm is about to be moved. Since such a foreign object may interfere with the movement of the rocker arm, it becomes difficult for the rocker arm to be smoothly moved to a desired position on the rocker arm shaft.
The present invention has been made to overcome such drawbacks. Accordingly, an object of the present invention is to achieve a smooth movement of a rocker arm in a valve-actuating system of an engine, in which the rocker arm is moved in the directions of the axis of the swing of the rocker arm so as to achieve a variable cam for opening and closing the engine valve.